1. Field of the Invention
The present invention relates to a beam deflection system and a color tube, and in particular, to a beam deflection system capable of correcting chromatic aberration of image on a color tube.
2. Description of the Related Art
In general, an electronic tube for color image display (hereinafter, referred to as a xe2x80x9ccolor tubexe2x80x9d) 100 comprises a main body 101 of the color tube including a neck 102 of a tube shape and a display unit 103, and a beam deflection system (hereinafter, referred to as a xe2x80x9cdeflection yokexe2x80x9d) 104 allocated outside of the main body 101, as shown in FIG. 8.
Three electron guns 105, which generate three electron beams E corresponding to the image signals of three light colors red (R), green (G) and blue (B) inside of the neck 102, are arranged in horizontal direction in the color tube 100.
Fluorescent dots R, G, B are formed on a front surface of the display unit 103. A predetermined image is displayed by scanning the electron beam E of each image signal to the dots.
Meanwhile, a deflection yoke 104 is provided around the color tube from the neck 102 to the display unit 103 of the main body 103 for deflecting the progress of the electron beam E to vertical and horizontal directions.
As shown in FIG. 8, the deflection yoke 104 comprises a pair of horizontal deflection coils 106 vertically facing with each other in a tube shape to have a diameter coaxially extended from the neck 102 to the display unit 103 with the axial line P of the main body 101 of the color tube, a pair of vertical deflection coils 108 oppositely distanced from each other in a horizontal direction around an external periphery of a coil separator 107, on an internal surface of which the horizontal deflection coils 106 are mounted, and a ferrite core 109 of a ring shape surrounding the pair of vertical deflection coils 108.
The pair of horizontal deflection coil 106 of the deflection yoke 104 deflect the electron beams to a horizontal direction by providing the progress of the electron beams E with a vertical magnetic field, while the pair of vertical deflection coils 108 deflect the electron beams E to a vertical direction by providing the progress of the electron beams E with a horizontal magnetic field.
The coil separator 107 separates the horizontal deflection coils 106 from the vertical deflection coils 108, and supports those coils so that the positions thereof may not be biased.
Meanwhile, the ferrite core 109 is for enhancing magnetic flux formed in the progress of the electron beams E by the horizontal deflection coils 106 and the vertical deflection coils 108.
The horizontal and vertical deflection coils have two types. One is a bend type having a portion, in which a tip line of the neck is wound up in a radial direction in a rotational shape with respect to the axial line. The other is a bendless type having no wound-up portion.
As described above, the deflection yoke is coaxial with the axial line P of the main body of the color tube, while the three electron guns provided inside of the main body of the color tube has a construction such that a central electron gun for G is positioned on the axial line, and the other electron guns for B and R are positioned at both sides thereof.
When the three electron beams R, G, B are deflected against each deflection yoke in horizontal and vertical directions, the focusing angles of the electron beams for B and R, the original scanning position of which are out of the axial line, are varied and scanned to the dots that are out of a predetermined fluorescent dot, so that a chromatic aberration of images is generated.
The chromatic aberration as described above is classified into two cases: The first case is when convergence is misaligned in a horizontal direction (in an H direction) on B and R of the screen surface as shown in FIG. 10 (hereinafter, referred to as an xe2x80x9cXH aberrationxe2x80x9d). The second case is when a vertical axis on B and R (a V axis) is inclined and crossed (hereinafter, referred to a xe2x80x9cYH crossxe2x80x9d) as shown in FIG. 11.
Another case is when convergence is misaligned in a vertical direction (in a V direction) on B and R of the screen surface as shown in FIG. 12 (hereinafter, referred to as an xe2x80x9cYV aberration).
Such kinds of chromatic aberration are attributable not only to the aberration between the electron beams and the axial line of the deflection yoke but also to an aberration or inclination, etc. of a bi-directional axis when the deflection yoke is mounted on the main body of the color tube. Thus, the chromatic aberration should be corrected by each color tube.
A method that has been conventionally considered especially to correct the YV aberration of the three kinds of chromatic aberration was to adjust the amount of current flowing in the vertical deflection coil or to adjust the horizontal magnetic field by means of a pair of correction coils facing in horizontal direction. In case of adjusting the amount of current flowing in the vertical deflection coil, however, a problem arises such that a deformation is enlarged due to inclination of the path of the central electron beam for G even if the YV aberration is corrected.
Another conventional method used for correction of the XH aberration was to mount iron flaps or correction flaps composed of ferrite core at left and right sides of the neck, and to move the positions thereof. When the correction coils are attached to the left and right sides of the neck to correct the YV aberration, the correction coils are interrupted by the correction flaps in view of their positions, and the effective scope of the correction flaps is limited. As a result, the correctional scope of the XH aberration becomes narrow.
Another method that has been suggested to avoid the interruption with the correction flaps for XH aberration was to install the correction coils for correction of the YV aberration at the neck in a vertical direction for the purpose of adjustment with a vertical magnetic field. However, the correction is limitedly achieved in any one case of either the YV aberration when the B image is outside and the R image is inside or the YV aberration when the R image is outside and the B image is inside to correspond to the connecting direction of the pair of coils. This means that the above method has a drawback of failing to satisfy the needs of bi-directionally correcting the YV aberration.
It is, therefore, an object of the present invention to provide an electron beam deflection system and a color tube using the same that can facilitate correction of the XH aberration with a simple structure and perfectly correct the bi-directional YV aberration.
To achieve the above objects, there is provided an electron beam deflection system positioned outside of a main body of a color tube having a neck, inside of which electron beams are arranged in a horizontal direction, and a display unit extended from the neck in its diameter for displaying images by means of electron beams scanned from the electron beams, the system comprising: a pair of horizontal deflection coils arranged to face with each other in a vertical direction; a pair of vertical deflection coils arranged to face with each other in a horizontal direction; and a pair of coils arranged to face with each other in a vertical direction outside of the neck, each of the coils including a correction coil in a diametric direction of the neck for generating a magnetic field in an opposite direction to the direction of correcting a YV aberration.
A first coil and a second coil constituting the correction coil are serially connected for generating magnetic fields in opposite directions. The phase of the connecting point between the first coil and the second coil is controlled by a variable resistor.
The first coil and the second coil constituting the correction coil comprise one or more coils on a core, and are serially connected at the respective ends thereof.
The present invention is characterized in that a pair of central beam correction coils are provided for correcting aberration of the electron beams from the central one of the electron guns, and each of the correction coil composed of the first and the second coils is provided inside of the respective correction coils of the central electron beam.
The present invention is also characterized by comprising an electron beam deflection system and a main body of a color tube.